In digital broadcast systems, streaming content, such as television programming, is transmitted to consumers in encrypted form. To view this content, consumers must purchase rights to do so. In return, paying consumers receive one or more keys to decrypt the content upon reception.
Examples of such systems include direct video broadcast (DVB) systems, such as DVB-T and DVB-C networks, where certain television programs may be broadcast in encrypted form and can be viewed for payment. The term conditional access (CA) is often used to describe the encryption/decryption solution. This solution typically involves a set top box (STB) at a consumer's premises that is equipped with a vendor-specific CA module. This CA module stores the keys and performs the decryption process.
IP datacast (IPDC) over DVB-H (i.e. digital video broadcast to handheld devices) network is a new system that provides for the broadcast of various types of content using Internet Protocol (IP) transmissions across DVB transport systems. A DVB-H network has a fixed total capacity. The channel's exact capacity depends on the employed modulation parameters. For DVB-H, capacity is typically between 5 and 15 megabits per second (Mbps) for mobile and indoor reception. In DVB-H, this total bandwidth is divided into a number of timeslice channels that each have a static bit rate to facilitate mobility and handover.
Providers of streaming content (e.g., broadcasters of television programs) often wish to supply potential consumers with previews of the content. Thus, while an entire television program is viewable only for payment, short previews of the program may be viewed free of charge.
Providing such previews is technically challenging because such content streams are typically broadcast encrypted. Current technical challenges involve broadcasting an unencrypted (or plaintext) content stream without duplicating the required broadcast bandwidth and limiting the preview to short time periods while giving consumers the chance to freely pick the time of their preview.